Fix service definition

[X-Coder264]

#350 broke the service definition while refactoring from the XML to the PHP format. The correct tag name is monolog.logger, not monolog.setLogger (https://github.com/symfony/monolog-bundle/blob/v4.0.1/src/DependencyInjection/Compiler/LoggerChannelPass.php#L41).

This then results with the following errors when building the Symfony container in my app:

In LoggerChannelPass.php line 100:

Monolog configuration error: The logging channel "snappy" assigned to the "main" handler does not exist.

In ContainerBuilder.php line 1048:

You have requested a non-existent service "monolog.logger.snappy".

[Chris53897]

Thanks @X-Coder264
Your changes looks correct